This invention relates to a locking universal joint. The joint of the present invention permits global, three-dimensional positioning of an object. The universal joint of the present invention may be used in series of singly to provide a mechanism for positioning and locking an object such as, for example, a headrest or a lamp, in any position within a spherical range.
The conventional universal joint was first developed by Robert Hooke in the seventeenth century and has remained essentially unchanged since then. It generally involves input and output U-shaped rotatable coupling members which are intertwined and connected by a pin. This kind of coupling allows for universal movement of the output shaft with respect to the input shaft. There have also been developed several devices for locking an articulated universal joint in a particular position. For example, in U.S. Pat. No. 4,157,876 a lockable, universally articulated joint used in an orthopedic appliance is disclosed. The lockable, articulated joint has a hollow ball, or spherical member, which fits into a socket. The ball is formed with a circular opening in which a locking member is retained. The locking member has a convex outer surface which engages the mating concave inner surface of the ball. A locking screw extends through the socket and is threaded into the locking member. When the locking screw is loose, the locking member allows universal articulation between the socket and the ball, while preventing separation of the two relatively movable members. When the locking screw is tightened, however, the screw forces the outer surface of the locking member against the inner surface of the ball, which in turn clamps the outer surface of the ball against the socket so that the ball and socket are locked in a fixed relationship. Such prior art devices, however, have been found not to provide the precise positioning and positive locking which is required in some contexts, such as when supporting a headrest used in neurological surgery.